YouTube has apparently changed all videos on its site to play in widescreen format. Because most videos on the site were originally uploaded in a ratio closer to 4:3 (the standard size used on non-HD televisions), most videos are playing with horizontal black bars on the side. Some videos (like this one) are taking advantage of the full space, but are shrunk down to the normal size when they’re embedded elsewhere.

It seems that YouTube is either doing A/B testing or that the changes haven’t propagated to all servers (if that’s even possible) – hard refreshing on videos seems to alternate between the standard video player and the widescreen one. But it’s a widespread change, as hundreds of tweets are pouring in in about the switch to widescreen.

Widescreen YouTube videos have been spotted before now and could be enabled using a tag in the video’s URL, but this seems to be the first time that the feature is activated by default. The change may be related to YouTube’s recent announcement of full-length films from MGM, which pits it directly against Hulu.

YouTube is by no means the first video site to go widescreen – Blip.tv (my favorite YouTube alternative) has long had the feature. And as the comments point out, sites like Vimeo and SmugMug already offer video in HD.

Update: YouTube has written about the change on its blog.